In the field of industrial can manufacture, it is typical that the finished product requires some form of decoration in the form of printed indicia. Specialist printing machines are known to provide continuous, mass printing onto cans at a high throughput. These printing machines are commonly known as “decorators” in the art. At the present time, there are two main decorator designs which are in common commercial use, although there are additional, smaller volume manufacturers as well. The two main designs are commonly known as the “Concord” and “Rutherford” machines. Although the precise constructional details of the Concord and Rutherford machines differ, in essence they use the same approach to printing onto cans. This approach is a variant of offset printing. More specifically, the decorators comprise a plurality of inkers. Each inker is associated with a different colour, and has a printing plate for that colour. Each inker is configured to distribute ink of the correct colour onto the printing plate. The printing plate has a raised portion corresponding to the desired image for the particular colour in question. It will be apparent that, for example, a six inker decorator machine can print six colours, and an eight inker decorating machine can print eight colours. The ink from the print plate of each inker is transferred onto the surface of one of a number of blankets. The intention is that the blanket and the print cylinders of all of the inkers are mutually positioned and oriented such that the different coloured inks are in proper registration. When proper registration is achieved, the pattern of multiply coloured inks on the blanket corresponds to the desired indicia. The decorator machines comprise a plurality of blankets which are disposed on a rotating blanket wheel. As the wheel rotates, a blanket which has had all of the inks transferred to it in the desired pattern is brought into contact with a suitable conveyor system which typically uses a number of mandrels on a mandrel wheel. The decorator machine is configured so that each can is brought into contact with a blanket so that the full multicoloured indicia is transferred to the surface of the can.
It is inevitable that during a continuous can printing process, some misregistration of one or more of the colours will occur. Traditionally, misregistration problems have been corrected manually. More specifically, any misregistration is detected by manual inspection of the printed cans. If a misregistration is identified, then it has been necessary to shut down printing for a period of time whilst manual adjustments of the inkers are made. This is an inefficient process for at least two reasons. Firstly, there is a time lag before a misregistration is identified which can result in can spoilage. Secondly, it is inefficient and undesirable to shut down a continuous process for any period of time.